Delta writing scheme for mimo signal paths

ABSTRACT

Techniques for writing to registers associated with MIMO signal paths are disclosed. In are embodiment, a controller writes a common value to all registers corresponding to the same operational parameter or parameters, for all signal paths in the MIMO transmitter or receiver. The controller then updates the register in any signal path whose operational paramater differs from the common value, by accumulating a value to the value already in the register, or by replacing the value already in the register with a different value.

TECHNICAL FIELD

The disclosure relates to communications signal processing, and moreparticularly, to signal processing techniques for multiple-inputmultiple-output (MIMO) systems.

BACKGROUND

In a wireless communication system, an RF modulated signal from atransmitter may reach a receiver via a number of propagation paths. Thecharacteristics of the propagation paths typically vary over time due toa number of factors such as fading and multipath. To provide diversityagainst deleterious path effects and improve performance, multipletransmit and receive antennas may be used. Generally, diversityincreases and performance improves with more transmit (TX) and receive(RX) antennas.

A multiple-input multiple-output (MIMO) communication system can employmultiple (M) transmit antennas and multiple (N) receive antennas fordata transmission. A MIMO channel formed by the M transmit and N receiveantennas may be decomposed into I independent channels, with 1<min {M,N}. Each of the 1 independent channels corresponds to a dimension, andmay also be referred to as a spatial subchannel (or a transmissionchannel) of the MIMO channel. The MIMO system can provide improvedperformance (e.g., increased transmission capacity) if the additionaldimensionalities created by the multiple transmit and receive antennasare utilized.

Every TX antenna in a MIMO system is usually provided with acorresponding TX signal path, which prepares a signal for transmissionover the TX antenna. For example, a TX signal path may include RFcircuitry for upconverting and amplifying a baseband TX signal.Similarly, every RX antenna in a MIMO system is usually provided with acorresponding RX signal path, which processes the signal received by theRX antenna. For example, a RX signal path may include RF circuitry foramplifying a received signal, and downconverting the signal to basebandfor further RX processing.

For each signal path (TX or RX), multiple parameters may need to beconfigured depending on the particular characteristics of that signalpath. For example, one such parameter may be a common-mode voltage trimparameter associated with a low-noise amplifier (LNA) in each RX signalpath. Given that there may be multiple such parameters per signal path,and multiple signal paths in a MIMO system, it would be desirable tohave efficient techniques to configure all the parameters of all thesignal paths in a MIMO system.

SUMMARY

One aspect of the disclosure provides a method for specifying aparameter for a plurality of signal paths, each signal pathcorresponding to an antenna for transmission or reception of signals, aset of registers associated with each signal path, the method comprisinga first step comprising writing a common value to a register associatedwith said parameter, the first step further comprising providing saidcommon value to all registers associated with said parameter in saidplurality of signal paths; and a second step comprising determiningwhether, for one of said signal paths, said parameter is associated witha value different from said common value, and if so, modifying theregister associated with said parameter in said one of said signalpaths.

Another aspect of the disclosure provides a computer program product forspecifying a parameter for a plurality of signal paths, each signal pathcorresponding to an antenna for transmission or reception of signals, aset of registers associated with each signal path, the productcomprising computer-readable medium comprising code for causing acomputer to write a common value to a register associated with saidparameter, the code further causing a computer to provide said commonvalue to all registers associated with said parameter in said pluralityof signal paths; and code for causing a computer to determine whether,for one of said signal paths, said parameter is associated with a valuedifferent from said common value, and if so, causing the computer tomodify the register associated with said parameter in said one of saidsignal paths.

Yet another aspect of the disclosure provides An apparatus forspecifying a parameter for a plurality of signal paths, each signal pathcorresponding to an antenna for transmission or reception of signals, aset of registers associated with each signal path, the apparatuscomprising means for writing a common value to a register associatedwith said parameter; means for providing said common value to allregisters associated with said parameter in said plurality of signalpaths; and means for determining whether, for one of said signal paths,said parameter is associated with a value different from said commonvalue, and if so, modifying the register associated with said parameterin said one of said signal paths.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a block diagram of a transmitter 110 and a receiver 150 fora MIMO transmission.

FIG. 2 depicts registers associated with transmitter units 118.1 through118.M, here labeled TMTR.1 through TMTR.M.

FIG. 3 depicts a prior art technique by which controller/processor 130configures in sequence the values of the registers shown in FIG. 2.

FIGS. 4A and 4B depict a two-step delta writing scheme according to thepresent disclosure for configuring registers in the transmitter units.

FIG. 4C depicts an embodiment wherein a value already in a register canbe accumulated with a given value.

DETAILED DESCRIPTION

Disclosed herein are efficient techniques for specifying the parametersof each signal path in a MIMO receiver or transmitter.

The techniques described herein may be used for various communicationsystems such as Code Division Multiple Access (CDMA) systems, TimeDivision Multiple Access (TDMA) systems, Frequency Division MultipleAccess (FDMA) systems, Orthogonal FDMA (OFDMA) systems, Single-CarrierFDMA (SC-FDMA) systems, etc. A CDMA system utilizes code divisionmultiplexing (CDM) and transmits modulation symbols in parallel usingdifferent channelization codes. A CDMA system may utilize a radiotechnology such as Wideband-CDMA (W-CDMA), cdma2000, etc. cdma2000covers IS-2000, IS-856, and IS-95 standards. A TDMA system may utilize aradio technology such as Global System for Mobile Communications (GSM).W-CDMA and GSM are described in documents from the “3rd GenerationPartnership Project” (3GPP). cdma2000 is described in documents from the“3rd Generation Partnership Project 2” (3GPP2). 3GPP and 3GPP2 documentsare publicly available. An OFDMA system utilizes orthogonal frequencydivision multiplexing (OFDM) and transmits modulation symbols in thefrequency domain on orthogonal subcarriers. An SC-FDMA system utilizessingle-carrier frequency division multiplexing (SC-FDM) and transmitsmodulation symbols in the time domain on orthogonal subcarriers.

The techniques described herein may also be used for MIMO transmittersand receivers for the downlink as well as the uplink. The downlink (orforward link) refers to the communication link from base stations towireless devices, and the uplink (or reverse link) refers to thecommunication link from the wireless devices to the base stations.

FIG. 1 shows a block diagram of a transmitter 110 and a receiver 150 fora MIMO transmission.

For downlink transmission, transmitter 110 is part of a base station,and receiver 150 is part of a wireless device. For uplink transmission,transmitter 110 is part of a wireless device, and receiver 150 is partof a base station. A base station is typically a fixed station thatcommunicates with the wireless devices and may also be called a Node B,an access point, etc. A wireless device may be stationary or mobile andmay also be called a user equipment (UE), a mobile station, a terminal,a station, a subscriber unit, etc. A wireless device may be a cellularphone, a personal digital assistant (PDA), a wireless modem, a laptopcomputer, a handheld device, etc.

Controllers/processors 130 and 180 direct operation of variousprocessing units at transmitter 110 and receiver 150, respectively.Memories 132 and 182 store data and program codes for transmitter 110and receiver 150, respectively.

At transmitter 110, a transmit data processor (TX Data Proc) 112receives traffic data and signaling, processes (e.g., encodes,interleaves, and symbol maps) the data, and provides data symbols.Processor 112 may also generate and multiplex pilot symbols with thedata symbols. As used herein, a data symbol is a symbol for traffic dataor signaling, a pilot symbol is a symbol for pilot, and a symbol istypically a complex value. The data symbols and pilot symbols may bemodulation symbols from a modulation scheme such as PSK or QAM. Pilot isdata that is known a priori by both the transmitter and receiver. A TXMIMO processor 114 performs spatial or spatio-temporal processing on thedata and pilot symbols and provides output symbols to multiple (M)modulators 116.1 through 116.M. Each modulator 116 modulates its outputsymbols and provides a modulated output to an associated transmitterunit (TMTR) 118.M modulated signals from M transmitter units 118.1through 118.M are transmitted from M antennas 120.1 through 120.M,respectively.

Each of transmitter units 118.1 through 118.M may have a plurality ofconfigurable parameters, e.g., parameters for trimming the electrical orother characteristics of the circuitry within each transmitter unit.Such parameters may include, for example, a TX gain control, a driveramplifier bias control, and TX baseband filter controls. Theseconfigurable parameters may be programmed by controller/processor 130.

At receiver 150, multiple (N) antennas 152.1 through 152.N receive thetransmitted signals via various propagation paths in the wirelessenvironment and provide N received signals to N receiver units (RCVR)154.1 through 154.N, respectively. Each receiver unit 154 processes(e.g., filters, amplifies, frequency downconverts, and digitizes) itsreceived signal and provides received samples to a channel processor 156and an equalizer/demodulator 160. Unit 160 provides filtered symbols. Areceive (RX) MIMO processor 170 combines the filtered symbols acrossspatial dimensions and provides detected symbols, which are estimates ofthe transmitted data symbols. An RX data processor 172 processes (e.g.,symbol demaps, deinterleaves, and decodes) the detected symbols andprovides decoded data. In general, the processing byequalizer/demodulator 160, RX MIMO processor 170, and RX data processor172 is complementary to the processing by modulator 116, TX MIMOprocessor 114, and TX data processor 112, respectively, at transmitter110.

Each of receiver units 154.1 through 154.N may have a plurality ofconfigurable parameters, e.g., parameters for trimming the electrical orother characteristics of the circuitry within each receiver unit. Suchparameters may include, for example, configuration parameters for alow-noise amplifier (LNA) such as a parameter controlling LNA currenttrimming in high-gain mode, a parameter controlling LNA common-modevoltage trimming, and a parameter controlling LNA gate voltage trimming.These configurable parameters may be programmed by controller/processor180.

In this specification and in the claims, a “signal path” may encompasscircuitry, registers, memory, etc., associated with a signal to betransmitted from a TX antenna, or a signal received from an RX antenna.Accordingly, a signal path may be a transmitter unit, a receiver unit, amodulator, or any sub-component thereof.

FIG. 2 depicts registers associated with transmitter units 118.1 through118.M, here labeled TMTR.1 through TMTR.M. Note that while theembodiment of FIG. 2 is described with respect to transmitter units, thetechniques disclosed may be readily applied to receiver units. Theapplication of the techniques described herein to receiver units will beclear to those of ordinary skill in the art in light of the presentdisclosure, and such embodiments are contemplated to be within the scopeof the present disclosure.

In FIG. 2, each transmitter unit is associated with a set of registerslabeled REG.1, REG.2, . . . , REG.X, where X is a variable representingthe number of registers per transmitter unit. Each register may containthe value of one or more of the operational parameters for thattransmitter unit.

According to the present disclosure, every transmitter unit may becharacterized by the same set of operational parameters. Therefore, thesame set of registers REG.1, . . . , REG.X is provided for eachtransmitter unit, as shown in FIG. 2. The value of each register may beset by the controller/processor 130.

FIG. 3 depicts a prior art technique by which controller/processor 130configures in sequence the values of the registers shown in FIG. 2. InFIG. 3, each register of each transmitter unit is separately addressed,and written to with a unique value. For example, a value value1_1 iswritten to register TMTR.1_REG.1, a value value1_2 is written toregister TMTR.1_REG.2, and so on, until all registers in all transmitterunits have been addressed and written to. According to thisimplementation, assuming that writing one value to one register requiresone write operation, then the number of write operations required toconfigure all the registers for all the transmitter units is M times X.Thus the number of required write operations scales linearly with thenumber of registers per transmitter unit, and the number of transmitterunits.

According to the present disclosure, the number of write operationsperformed by the controller/processor 130 as depicted in FIG. 3 may bereduced by assuming that the same parameter often takes on identicalvalues across transmitter units.

FIGS. 4A and 4B depict a two-step delta writing scheme according to thepresent disclosure for configuring registers in the transmitter units.Unless otherwise noted, the same techniques may be readily applied toreceiver units and their associated registers.

In the first step of the delta writing scheme, depicted in FIG. 4A, asingle value value1 is written to REG.1 of all transmitter units, i.e.,to TMTR.1_REG.1, TMTR.2_REG.1, . . . , TMTR.M_REG.1. Similarly, a singlevalue of value2 is written to REG.2 of all transmitter units, and asingle value of value3 is written to REG.3 of all transmitter units,etc., until all registers for all transmitter units have been writtento. Assuming that writing a single value to the same register ofmultiple transmitter units requires only one write operation, then thenumber of write operations required to configure all the registers forall the transmitter units according to the first step of the deltawriting scheme is X. Note that the number of write operations does notscale with the number of transmitter units M.

In an embodiment, one write operation may supply a single value tomultiple registers as follows. First, the controller/processor 130outputs the desired value to a common bus shared among all registers inall transmitter units. Then, at the appropriate time, the bus value islatched to the designated register of all transmitter units. In thisway, a single value may be simultaneously written to the registers ofall transmitter units.

In an embodiment, controller/processor 130 writes a value to a registerin a transmitter unit, during a period when all transmitter units are ina “public write” mode. In the public write mode, a value written to oneregister in one transmitter unit is automatically copied to thecorresponding register in all other transmitter units. Thus, only onewrite operation is required to specify a value to the same register inall transmitter units in the public write mode.

FIG. 4B depicts a second step of the scheme according to the presentdisclosure for writing to registers in the transmitter units. The secondstep modifies, if necessary, the values written to the registers in thefirst step (depicted in FIG. 4A) of the delta writing scheme.

In FIG. 4B, a value delt1_1 is written to the register TMTR.1_REG.1 onlyif the register TMTR.1_REG.1 needs to be modified. Thus the valuedelt1_1 replaces the value written to TMTR.1_REG.1 during the first stepshown in FIG. 4A, i.e., “if necessary” as designated in FIG. 4B.According to the present disclosure, the condition “if necessary” maycorrespond to the case where the actual value for the operationalparameter of transmitter unit 1 differs from the value written to theregister TMTR.1_REG.1 during the first step shown in FIG. 4A. In thiscase, if the register TMTR.1_REG.1 does not need to be modified, then nowrite operation is performed.

Similarly, a value deltm_x may be written to a register TMTR.m_REG.x,but only if such register needs to be modified from the first step. Inthis way, a write operation is performed only “if necessary,” i.e., ifthe value for an operational parameter of a transmitter unit isdifferent from the common value written to the corresponding registerduring the first step of the delta writing scheme.

In an embodiment, values in the second step can be written to registersin a “private write” mode, wherein a value written to one register inone transmitter will not be written to the corresponding register in allother transmitters. This contrasts with the “public write” modedescribed above with reference to FIG. 4A. In this embodiment, the firststep depicted in FIG. 4A is performed in public write mode, while thesecond step depicted in FIG. 4B is performed in the private write mode.

Assuming that, in MIMO systems, the value of a single configurableparameter is often identical across multiple transmitter units, then notall registers will need to be written to during the second step.Accordingly, the number of write operations needed to configure all theregisters in all the transmitter units will likely be less than the Mtimes X operations required by the prior art implementation depicted inFIG. 3.

As an example of the possible efficiency gain of the disclosed deltawriting scheme, assume that a two-transmit antenna MIMO system includestwo transmitter units, each transmitter unit having ten registers forstoring the configurable parameters of the transmitter unit. Furtherassume that the two transmitter units share identical values for nine ofthe registers. According to the prior art scheme depicted in FIG. 3, thecontroller/processor 130 would perform twenty write operations tospecify all the parameters for all the transmitter units. In contrast,according to the delta writing scheme depicted in FIGS. 4A and 4B, onlyeleven write operations would be needed to specify all parameters: tenwrite operations according to the first step, and one write operationaccording to the second step to specify one value for the register notsharing a common value between the two transmitter units.

In an embodiment, the second step of the delta writing scheme need notoverwrite the value already in a register, as shown in FIG. 4B. Rather,as shown in FIG. 4C, the value already in a register can be accumulatedwith a value already in the register. This and other modifications tothe disclosure will be clear to one of ordinary skill in the art, andare contemplated to be within the scope of the present disclosure.

In an embodiment, the delta writing scheme can be applied to parametersother than those characterizing the electrical circuitry of the TX or RXsignal paths. For example, a register specifying power control commandsto be sent over the air for a TX signal path may be configured accordingto the scheme disclosed herein. One of ordinary skill in the art willrealize that any parameter associated with transmitter or receiver unitsmay be configured according to the scheme disclosed herein. Embodimentsfor configuring such other parameters are contemplated to be within thescope of the present disclosure.

While embodiments of the present disclosure have been described withrespect to MIMO systems, application to any transmitter or receiveremploying multiple antennas and signal paths is contemplated to bewithin the scope of the present disclosure. For example, the techniquescan be applied to configure registers for multiple TX signal paths in atransmitter employing antenna transmit diversity.

Based on the techniques described herein, it should be apparent that anaspect disclosed herein may be implemented independently of any otheraspects and that two or more of these aspects may be combined in variousways. Aspects of the techniques described herein may be implemented inhardware, software, firmware, or any combination thereof. If implementedin hardware, the techniques may be realized using digital hardware,analog hardware or a combination thereof. If implemented in software,the techniques may be realized at least in part by a computer programproduct that includes a computer readable medium on which one or moreinstructions or code is stored.

By way of example, and not limitation, such computer-readable media cancomprise RAM, such as synchronous dynamic random access memory (SDRAM),read-only memory (ROM), non-volatile random access memory (NVRAM), ROM,electrically erasable programmable read-only memory (EEPROM), erasableprogrammable read-only memory (EPROM), FLASH memory, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other tangible medium that can be used to carry or storedesired program code in the form of instructions or data structures andthat can be accessed by a computer.

The instructions or code associated with a computer-readable medium ofthe computer program product may be executed by a computer, e.g., by oneor more processors, such as one or more digital signal processors(DSPs), general purpose microprocessors, ASICs, FPGAs, or otherequivalent integrated or discrete logic circuitry.

In this specification and in the claims, it will be understood that whenan element is referred to as being “connected to” or “coupled to”another element, it can be directly connected or coupled to the otherelement or intervening elements may be present. In contrast, when anelement is referred to as being “directly connected to” or “directlycoupled to” another element, there are no intervening elements present.

A number of aspects and examples have been described. However, variousmodifications to these examples are possible, and the principlespresented herein may be applied to other aspects as well. These andother aspects are within the scope of the following claims.

1. A method for specifying a parameter for a plurality of signal paths,each signal path corresponding to an antenna for transmission orreception of signals, a set of registers associated with each signalpath, the method comprising: a first step comprising writing a commonvalue to all registers associated with said parameter in said pluralityof signal paths; and a second step comprising determining whether, forone of said signal paths, said parameter is associated with a valuedifferent from said common value, and if so, modifying the registerassociated with said parameter in said one of said signal paths.
 2. Themethod of claim 1, the writing a common value comprising writing a valueto a register in a public write mode.
 3. The method of claim 2, themodifying comprising writing to a register in a private write mode. 4.The method of claim 1, the plurality of signal paths comprising aplurality of transmitter signal paths.
 5. The method of claim 1, theplurality of signal paths comprising a plurality of receiver signalpaths.
 6. The method of claim 1, the parameter being a trimming voltage.7. The method of claim 1, the writing a common value comprising:outputting the common value onto a bus; and latching the common valuefrom said bus into all registers associated with said parameter.
 8. Themethod of claim 1, the modifying comprising accumulating a value to avalue already in the register in said one of said signal paths.
 9. Themethod of claim 1, the modifying comprising replacing a value already inthe register in said one of said signal paths with a different value.10. A computer program product for specifying a parameter for aplurality of signal paths, each signal path corresponding to an antennafor transmission or reception of signals, a set of registers associatedwith each signal path, the product comprising: computer-readable mediumcomprising: code for causing a computer to write a common value to allregisters associated with said parameter in said plurality of signalpaths; and code for causing a computer to determine whether, for one ofsaid signal paths, said parameter is associated with a value differentfrom said common value, and if so, causing the computer to modify theregister associated with said parameter in said one of said signalpaths.
 11. The computer program product of claim 10, the code forcausing a computer to write a common value comprising code for causingthe computer to write a value to a register in a public write mode. 12.The computer program product of claim 11, the code for causing acomputer to modify comprising code for causing a computer to write to aregister in a private write mode.
 13. The computer program product ofclaim 10, the plurality of signal paths comprising a plurality oftransmitter signal paths.
 14. The computer program product of claim 10,the plurality of signal paths comprising a plurality of receiver signalpaths.
 15. The computer program product of claim 10, the parameter beinga trimming voltage.
 16. The computer program product of claim 10, thecode for causing a computer to write causing the computer to: output thecommon value onto a bus; and latch the common value from said bus intosaid registers associated with said parameter.
 17. The computer programproduct of claim 10, the code for causing a computer to modify causingthe computer to accumulate a value to a value already in the register insaid one of said signal paths.
 18. The computer program product of claim10, the code for causing a computer to modify causing the computer toreplace a value already in the register in said one of said signal pathswith a different value.
 19. An apparatus for specifying a parameter fora plurality of signal paths, each signal path corresponding to anantenna for transmission or reception of signals, a set of registersassociated with each signal path, the apparatus comprising: means forwriting a common value to all registers associated with said parameterin said plurality of signal paths; and means for determining whether,for one of said signal paths, said parameter is associated with a valuedifferent from said common value, and if so, modifying the registerassociated with said parameter in said one of said signal paths.
 20. Theapparatus of claim 19, the means for writing a common value comprisingmeans for writing a value to a register in a public write mode.
 21. Theapparatus of claim 20, the means for modifying comprising means forwriting to a register in a private write mode.
 22. The apparatus ofclaim 19, the plurality of signal paths comprising a plurality oftransmitter signal paths.
 23. The apparatus of claim 19, the pluralityof signal paths comprising a plurality of receiver signal paths.
 24. Theapparatus of claim 19, the parameter being a trimming voltage.
 25. Theapparatus of claim 19, the means for writing a common value comprising:means for outputting the common value onto a bus; and means for latchingthe common value from said bus into all registers associated with saidparameter.